One of the most complete catalogs of white dwarf stars that have exploded ever compiled is providing new clues about the nature of dark energy, the mysterious force that is driving the accelerated expansion of the Universe.
Led by researchers from the School of Mathematics and Physics at the University of Queensland, in Australia, the work brings together data from 2,884 Type Ia supernovae, used by astronomers to measure cosmic distances. The data set allows tracing with greater precision the evolution of the expansion of the Universe over time.
“We reconstructed three decades of astronomical observations into a single consistent framework,” explains Ryan Camilleri, a PhD student and the paper’s lead author.
The researchers combined the supernova data with other cosmological measurements, including the relic light from the Big Bang and the maps of the distribution of galaxies in space.
The results do not, however, confirm the standard cosmological model, which assumes that dark energy is a constant and does not change over time. On the contrary, the data point to the possibility that dark energy evolves.
“Rather than confirming the standard cosmological model, which assumes dark energy is fixed and does not change, we have more evidence that dark energy may change over time,” says Ryan Camilleri.
Three decades of observations revised
The new catalog includes historical measurements and data from the Dark Energy Survey (DES), published in 2024. To make observations conducted over several decades comparable, the researchers reanalyzed the oldest data using modern techniques.
“Over the years we have learned much more about the behavior of supernovae, so we were able to go back to the older data and apply that improved knowledge to it,” explains Camilleri.
The team also sought to standardize observations from different telescopes and with varying capabilities, taking into account factors that can alter the light emitted by a supernova, such as cosmic dust and the mass of galaxies.
Subtle effects were also considered, such as gravitational lensing, the phenomenon by which light is deflected and magnified as it passes near massive objects before reaching Earth.
Independent hints of a variable dark energy
Tamara Davis, an astrophysicist and professor at the University of Queensland, regards the new catalog as an important step toward understanding the nature of dark energy.
“Our DES supernova data, in 2024, showed for the first time hints that dark energy may vary over time, and this new compilation also identifies a deviation from the standard model, though in a slightly different direction,” she says.
Findings from the Dark Energy Spectroscopic Instrument (DESI) have also identified hints of variations in dark energy, through the study of the so-called fossil acoustic waves of the primordial Universe.
“Thus, two completely independent measurements found evidence of a time variation of dark energy, challenging the standard model in which dark energy does not change,” the researcher underlines.
Although these results do not yet allow a definitive conclusion that dark energy varies over time, the data mainly provide new hints that will need to be tested with future observations.
The issue could have implications that reach beyond cosmology. According to Tamara Davis, a better understanding of dark energy could also help clarify the relationship between gravity and quantum physics.
“We know these two theories are extremely successful in their respective domains, so if we can figure out how to reconcile them, it would be a huge step in theoretical physics,” she says.
More supernovae will bolster the investigation
The catalog is expected to keep growing as new astronomical surveys are incorporated. Among them is the Dark Energy Bedrock All-Sky Supernova program (DEBASS), which is already detecting hundreds of new supernovae closer to Earth than those observed by the Dark Energy Survey.
The work results from the collaboration of hundreds of researchers over several decades, involving projects such as the Dark Energy Survey, Foundation Supernova Survey, Pan-STARRS1, Sloan Digital Sky Survey, Supernova Legacy Survey and Carnegie Supernova Project, among others.
The cosmological results were made available on the arXiv, as were the measurements of the masses of the host galaxies of the supernovae.
